import 'dart:async';
import 'dart:io';
import 'dart:typed_data';

import 'package:aves/services/cast/cast_fmp4_fragment_parser.dart';

class CastFmp4ProgressiveReaderException implements Exception {
  final String message;

  const CastFmp4ProgressiveReaderException(
    this.message,
  );

  @override
  String toString() {
    return 'CastFmp4ProgressiveReaderException: $message';
  }
}

class CastFmp4ProgressiveReader {
  CastFmp4ProgressiveReader({
    required this.sourcePath,
    required this.pollingInterval,
    required this.onFragment,
  });

  final String sourcePath;
  final Duration pollingInterval;

  final Future<void> Function(
    Fmp4FragmentInfo fragment,
  )
  onFragment;

  final CastFmp4FragmentParser _parser = const CastFmp4FragmentParser();

  final Map<int, int> _decodeTimes = <int, int>{};

  RandomAccessFile? _source;

  bool _running = false;
  bool _stopRequested = false;
  bool _conversionCompleted = false;

  int _nextOffset = 0;
  int _fragmentCount = 0;

  _PendingMoof? _pendingMoof;

  bool get isRunning => _running;

  int get fragmentCount => _fragmentCount;

  Map<int, int> get decodeTimes => Map<int, int>.unmodifiable(_decodeTimes);

  Future<void> start() async {
    if (_running) {
      throw const CastFmp4ProgressiveReaderException(
        'Lettore fMP4 già in esecuzione',
      );
    }

    _running = true;
    _stopRequested = false;

    try {
      await _run();
    } finally {
      _running = false;
      await _closeSource();
    }
  }

  void notifyConversionCompleted() {
    _conversionCompleted = true;
  }

  void requestStop() {
    _stopRequested = true;
  }

  Future<void> _run() async {
    final file = File(sourcePath);

    while (!_stopRequested) {
      if (!await file.exists()) {
        if (_conversionCompleted) {
          throw CastFmp4ProgressiveReaderException(
            'File fMP4 non trovato: $sourcePath',
          );
        }

        await Future<void>.delayed(
          pollingInterval,
        );
        continue;
      }

      _source ??= await file.open(
        mode: FileMode.read,
      );

      final progressed = await _consumeAvailableBoxes(
        file,
      );

      if (progressed) {
        continue;
      }

      if (_conversionCompleted) {
        final fileLength = await file.length();

        if (_nextOffset != fileLength) {
          throw CastFmp4ProgressiveReaderException(
            'Conversione terminata con box incompleto: '
            'nextOffset=$_nextOffset '
            'fileLength=$fileLength',
          );
        }

        if (_pendingMoof != null) {
          throw const CastFmp4ProgressiveReaderException(
            'Conversione terminata con moof senza mdat',
          );
        }

        return;
      }

      await Future<void>.delayed(
        pollingInterval,
      );
    }
  }

  Future<bool> _consumeAvailableBoxes(
    File file,
  ) async {
    var progressed = false;

    while (!_stopRequested) {
      final fileLength = await file.length();

      final header = await _readBoxHeader(
        fileLength,
      );

      if (header == null) {
        break;
      }

      if (header.end > fileLength) {
        break;
      }

      await _consumeBox(header);

      _nextOffset = header.end;
      progressed = true;
    }

    return progressed;
  }

  Future<_BoxHeader?> _readBoxHeader(
    int fileLength,
  ) async {
    const normalHeaderSize = 8;

    if (fileLength - _nextOffset < normalHeaderSize) {
      return null;
    }

    final source = _source;

    if (source == null) {
      return null;
    }

    await source.setPosition(_nextOffset);

    final normalHeader = await source.read(
      normalHeaderSize,
    );

    if (normalHeader.length != normalHeaderSize) {
      return null;
    }

    final normalData = ByteData.sublistView(
      Uint8List.fromList(normalHeader),
    );

    final size32 = normalData.getUint32(
      0,
      Endian.big,
    );

    final type = String.fromCharCodes(
      normalHeader.sublist(4, 8),
    );

    var headerSize = normalHeaderSize;
    late final int size;

    if (size32 == 1) {
      if (fileLength - _nextOffset < 16) {
        return null;
      }

      final extendedBytes = await source.read(
        8,
      );

      if (extendedBytes.length != 8) {
        return null;
      }

      size =
          ByteData.sublistView(
            Uint8List.fromList(extendedBytes),
          ).getUint64(
            0,
            Endian.big,
          );

      headerSize = 16;
    } else if (size32 == 0) {
      if (!_conversionCompleted) {
        return null;
      }

      size = fileLength - _nextOffset;
    } else {
      size = size32;
    }

    if (size < headerSize) {
      throw CastFmp4ProgressiveReaderException(
        'Dimensione box non valida: '
        'offset=$_nextOffset '
        'type=$type '
        'size=$size',
      );
    }

    return _BoxHeader(
      offset: _nextOffset,
      size: size,
      headerSize: headerSize,
      type: type,
    );
  }

  Future<void> _consumeBox(
    _BoxHeader header,
  ) async {
    switch (header.type) {
      case 'ftyp':
      case 'moov':
        return;

      case 'moof':
        _consumeMoof(header);
        return;

      case 'mdat':
        await _consumeMdat(header);
        return;

      default:
        return;
    }
  }

  void _consumeMoof(
    _BoxHeader header,
  ) {
    if (_pendingMoof != null) {
      throw CastFmp4ProgressiveReaderException(
        'Nuovo moof prima del relativo mdat: '
        'offset=${header.offset}',
      );
    }

    _pendingMoof = _PendingMoof(
      offset: header.offset,
      size: header.size,
    );
  }

  Future<void> _consumeMdat(
    _BoxHeader header,
  ) async {
    final pending = _pendingMoof;

    if (pending == null) {
      throw CastFmp4ProgressiveReaderException(
        'mdat senza moof: '
        'offset=${header.offset}',
      );
    }

    if (pending.end != header.offset) {
      throw CastFmp4ProgressiveReaderException(
        'moof e mdat non adiacenti: '
        'moofEnd=${pending.end} '
        'mdatOffset=${header.offset}',
      );
    }

    final moofBytes = await _readRange(
      offset: pending.offset,
      length: pending.size,
    );

    final fragment = _parser.parse(
      moofBytes: moofBytes,
      moofOffset: pending.offset,
      mdatOffset: header.offset,
      mdatSize: header.size,
      mdatHeaderSize: header.headerSize,
      initialDecodeTimes: Map<int, int>.from(_decodeTimes),
    );

    for (final track in fragment.tracks) {
      _decodeTimes[track.trackId] = track.nextDecodeTime;
    }

    await onFragment(fragment);

    _fragmentCount++;
    _pendingMoof = null;
  }

  Future<Uint8List> _readRange({
    required int offset,
    required int length,
  }) async {
    final source = _source;

    if (source == null) {
      throw const CastFmp4ProgressiveReaderException(
        'File fMP4 non aperto',
      );
    }

    await source.setPosition(offset);

    final bytes = await source.read(length);

    if (bytes.length != length) {
      throw CastFmp4ProgressiveReaderException(
        'Lettura incompleta: '
        'offset=$offset '
        'actual=${bytes.length} '
        'expected=$length',
      );
    }

    return Uint8List.fromList(bytes);
  }

  Future<void> _closeSource() async {
    final source = _source;
    _source = null;

    if (source != null) {
      await source.close();
    }
  }
}

class _PendingMoof {
  final int offset;
  final int size;

  const _PendingMoof({
    required this.offset,
    required this.size,
  });

  int get end => offset + size;
}

class _BoxHeader {
  final int offset;
  final int size;
  final int headerSize;
  final String type;

  const _BoxHeader({
    required this.offset,
    required this.size,
    required this.headerSize,
    required this.type,
  });

  int get end => offset + size;
}